Metal defect detection method of laser-electromagnetic ultrasonic nondestructive testing system

Abstract

The invention relates to a metal defect detection method of a laser-electromagnetic ultrasonic nondestructive testing system. The method adopts the laser-electromagnetic ultrasonic testing system composed of a pulsed laser, a linear focusing unit, a transverse wave electromagnetic ultrasonic sensor, a three-dimensional mechanical stepping device, a signal amplification filtering system, a digital oscilloscope and a computer. The system is utilized to excite a Gaussian laser pulse, which is then delivered to the surface of a metal material through an optical focusing system, and at the same time surface waves as well as transverse waves are excited. The transverse wave electromagnetic ultrasonic sensor is used for receiving, and on the basis, positioning detection of the surface and near surface defects can be performed. The method makes use of the transverse wave electromagnetic ultrasonic sensor to receive diffraction transverse waves generated when the transverse waves encounter an internal defect, and when the sensor is position right above a metal material internal defect, the received diffraction transverse wave signal has the strongest amplitude, so that the horizontal position of the defect can be determined, and the vertical position of the defect can be determined by the defect echo time. The method can realize detection of metal material surface, near surface and internal defects at the same time.

Description

technical field

[0001] The invention relates to a metal defect detection method of a laser-electromagnetic ultrasonic nondestructive testing system, belonging to the field of ultrasonic nondestructive testing and evaluation. Background technique

[0002] So far, no practical method of non-contact ultrasonic diffraction detection based on laser-electromagnetic ultrasonic technology that can be applied to metal material defects has been seen. The ultrasonic diffraction method has the advantages of high detection accuracy and fast speed when detecting material defects. At present, since most ultrasonic diffraction methods used to detect internal defects of materials are based on contact piezoelectric ultrasonic technology, the detection sensitivity is greatly affected by the coupling state. In the article "Time-of-Flight Diffraction Measurement Using Laser Ultrasound", Mihara proposed that laser can be used to excite ultrasonic waves and combined with laser interferometer to r...

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